An example of a conventional automatic cooking apparatus for a microwave oven on the basis of a determination of the type of food is shown in U.S. Pat. No. 4,831,239, issued May 16, 1989, and the arrangement thereof is shown in block form in FIG. 1 herein. As shown in FIG. 1, the conventional automatic cooking apparatus comprises a heating chamber 3 for containing food 4, to be cooked, for heating thereof for heating thereof, a turntable 5 disposed in the heating chamber 3, and on the bottom thereof, a turntable motor 6 placed below the heating chamber 3 for rotating the turntable 5, a weight sensor 7 is disposed below the turntable motor 6 for sensing the weight of the food 4, a weight detection circuit 8 is provided for generating an electrical signal corresponding to the weight of the food 4 sensed by the weight sensor 7, and a magnetron 9 is placed on the top of the heating chamber 3 for radiating microwave energy into the heating chamber 3, a cooling fan 10 is disposed at one side of the magnetron 9 for blowing cooling air to cool the magnetron 9, and an intake guide 12 is disposed at the other side of the magnetron 9 on top of the heating chamber 3 for introducing a part of the cooling air blown from the cooling fan 10 into the heating chamber 3, an exhaust guide 14 is placed on a side wall of the heating chamber 3 for exhausting vapor and various gases generated from the heated food 4 in the heating chamber 3 to the outside, and a gas sensor 15 is provided in the exhaust guide 14 for sensing the amount of the vapor and gases being exhausted to the outside, a gas detection circuit 16 is provided for generating an electrical signal corresponding to the amount of vapor and gases sensed by the gas sensor 15, and an ultrasonic sensor 17, is provided on the ceiling of the heating chamber 3 for transmitting an ultrasonic wave toward the food 4 and receiving an echo wave returning therefrom to measure the distance to the food 4, a drive and detection circuit 18 is provided for driving the ultrasonic sensor 17 and generating an electrical signal corresponding to the distance to the food 4 measured by the ultrasonic sensor 17, and an automatic cooking control section 1 is provided for determining the of food 4 on the basis of the detected values from the drive and detection circuit 18, the weight detection circuit 8 and the gas detection circuit 16, and for controlling the automatic cooking of the food 4 in accordance with determined type of the food 4, a driver 13 is provided for driving the magnetron 9 and the turntable motor 6 under the control of the automatic cooking control section 1, and a keyboard 2 is provided for providing key inputs to the automatic cooking control section 1.
The operation of the conventional automatic cooking apparatus with the above-mentioned construction will now be described.
In operation, when the user turns on the microwave oven, places the food 4 to be cooked on the turntable 5 in the heating chamber 3 and operates keys of the keyboard 2 to start the automatic cooking of the food 4, the control section 1 starts the automatic cooking control.
That is, the control section 1 actuates the driver 13 to drive the turntable motor 6, in response to a cooking start signal which was input through the keyboard 2. The turntable 5 is rotated according to the driving of the turntable motor 6. At this time, the weight sensor 7 senses the weight of the food 4 and an electrical signal corresponding to the sensed weight is generated in the weight detection circuit 8, which then supplies the weight signal to the control section 1 as cooking information.
At the same time, the control section 1 controls the drive and detection circuit 18 to energize the ultrasonic sensor 17, so that the ultrasonic sensor 17 emits the ultrasonic wave to the food 4 placed on the turntable 5 to measure the distance to the food 4 by reception of an echo wave returning from the surface of the food 4. The distance d from the surface of the food 4 to the ultrasonic sensor 17 is determined on the basis of a time difference between the transmission and reception of the ultrasonic wave, and signal indicative of the distance data is supplied from the drive and detection circuit 18 to the control section 1.
In the control section 1, the weight W of the food 4 is calculated according to the weight detected signal from the weight detection circuit 8, and the height h thereof is calculated by subtracting the distance from the distance H between the ultrasonic sensor 17 and the top surface of the turntable 5. Namely, the height h of the food 4 is obtained as h=H-d.
Then, in the control section 1, the volume V of the food 4 is determined on the basis of the calculated height h, and the density D is calculated on the basis of the determined volume V and weight W. Namely, the density D of the food 4 positioned on the turntable 5 is obtained as D=W/V.
Accordingly, the control section 1 determines the type of food 4 on the basis of the calculated density D of the food 4 and performs the automatic cooking control in accordance with that determination. Namely, the control section 1 pre-stores, in the form of a look-up table in its memory, appropriate automatic cooking control values (heating time periods) corresponding to the densities of various foods and, with the density of the food to be cooked calculated, reads the automatic cooking control value corresponding to the calculated density of the food from the pre-stored look-up table in its memory and performs the automatic cooking control on the basis of the read value read.
In accordance with the determination of the type of food 4 to be cooked, the control section 1 actuates the driver 13 on the basis of the corresponding automatic cooking control value, thereby causing the magnetron 9 to be driven to heat the food 4. The turntable motor 6 is also driven by the driver 13 and the turntable 5 is rotated according to the driving of the turntable motor 6. As a result, the food 4 is heated, while being rotated with the rotation of the turntable 5.
In response to the heating, the cooling fan 10 is driven to cool the magnetron 9 and the cooling air is introduced through the intake guide 12 into the heating chamber 3 which is in turn ventilation. After ventilated, the introduced air is exhausted through the exhaust guide 14 to the outside. The gas sensor 15 provided in the exhaust guide 14 senses the vapor and various gases generated from the heated object 4. The gas data from the gas sensor 15 is supplied through the gas detection circuit 16 to the control section 5. As a result, the control section 1 determines a cooking completion point of time on the basis of the gas data from the gas detection circuit 16 and completes the automatic cooking control operation at that time.
However, the above-mentioned conventional automatic cooking apparatus for the microwave oven has a disadvantage, in that the height of the food placed on the turntable is measured with the rotation thereof. In other words, the accurate measurement of the food height is difficult because of unreliability in the transmission and reception of the ultrasonic wave depending on the surface conditions of the food. Also, the control section is required to have high-performance operating ability, since the volume of the food must be determined on the basis of the measured height thereof and the density thereof must be calculated on the basis of the determined volume and weight thereof, eventhough the height of the food has been measured accurately. This requirement results in an increase in the cost of products.
Moreover, since the heating time period is determined only on the basis of the calculated density regardless of whether the food to be cooked is in the single or mixed form, a half-done or over-done case may occur in the mixed form of the food.
Further, an error in the calculated volume of the food and therefore an error in the calculated density thereof may occur due to a container placed on the turntable to contain the food. Also in calculating the density of food containing a large amount of water, there may occur a wide error due to different weights depending on the amount of contained water. These errors cause misrecognition of the type of food, thereby resulting in the erroneous automatic cooking control operation.
As a result, in the above-mentioned conventional automatic cooking apparatus for the microwave oven, the misrecognition of the food type and the resulting erroneous automatic cooking control operation occur frequently, resulting in decreased reliability of cooking according to the automatic control.